NINE hundred pesos, or $150, is the price the bird vendor quotes for the pair of toucans cowering in a tiny cage in Mexico City's Sonora Market. Inquiries about the two black birds, with their signature yellow-green beaks, appear to make the vendor both hopeful and nervous - which is understandable. Native to the jungles of southeast Mexico, toucans are a threatened species whose capture and sale is forbidden. And since Mexican environmental authorities raided the market that local environmentalists call the ''market of shame'' only four days earlier in July - taking away 1,104 animals, including three toucans - the bird vendor is being careful. ''So do you want them or not?'' he asks. ''You can take these, or if you want to think about it come back. I can always get more, no problem.'' Until there are no more toucans, he is probably right. Those two toucans, trembling and bleeding, symbolize the multibillion-dollar trafficking in the world's birds, mammals, reptiles, and insects that is impoverishing forests and open spaces at a rate second only to that caused by the destruction of habitat. Much of the trade is illegal but operates with widespread impunity. The forests of Africa, Latin America, and Asia are satisfying the world's urban dwellers' growing desire to possess a piece of disappearing nature. The rarer the better. While figures on the trade are only guesses, experts have no doubts about its cost. ''Whether the illicit animal trade comes in second in international ranking to drugs or third after arms is not really important,'' says Jacques Berney, deputy secretary general of the United Nations-administered Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in Geneva. ''What is important is that many of these animals are traded as extremely high-value goods, while countries are losing their natural wealth and at very little economic benefit.'' Conservative estimates place the annual global animal trade at $10 billion, with at least a third of that in prohibited species. Seemingly insatiable demand in Europe, the United States, and Japan teams up with attractive profits to keep the trade going despite national laws and international regulatory efforts, such as the 128-country CITES. With a rare Mexican or Brazilian parrot that the poacher receives a few dollars for in the jungle netting its final seller in Miami up to $20,000, the incentives are obvious. ''The profit margins in the illegal animal trade are comparable to the drug trade, but the risks involved are much less because penalties are much less. And there's very little punishment,'' says Ginette Hemley, director of international wildlife policy for the World Wildlife Fund in Washington. In fact the common routes used for international animal trafficking and frequent anecdotal evidence - such as dried armadillos found stuffed with cocaine, or boa constrictors carrying balloons filled with powdered heroin - suggest close coordination with the drug trade. And a number of drug kingpins are known to keep regular zoos of endangered species Most captured animals die enroute As concern about biodiversity and threatened species has grown over recent years, most attention has focused on habitat loss. But some experts like Ms. Hemley emphasize animal trade is now the principal threat to a growing number of species - including Africa's rhino, Asian tigers, and some highly marketable birds, such as macaws. Part of the reason is the means of capture and transport. Trees with nests of prized birds are cut down to retrieve the nestlings. Adult primates - like Mexico's spider monkeys or Indonesia's orangutans - are killed to facilitate the collection of their babies. Then the animals are transported in car trunks or concealed boxes. The result is that 85 percent of all captured animals die before even reaching the market, Mexican environmental authorities estimate. While such scenarios offer a grim picture of the trend in animal trafficking, experts point to a number of recent successes. International awareness campaigns have successfully cut the ivory trade and helped dry up the market for spotted-cat pelts. The US Wild Bird Conservation Act of 1992 reduced bird importation into the US by expanding the number of species banned from commercial trade. In terms of countries, CITES points to Italy. Only a few years ago it was considered a ''bad boy'' of the international animal and animal-products (pelts and skins) trade with virtually no control on illegal imports. Today it's a model of enforcement. ''Italy was for years a kind of laundering center, importing illegal reptile skins and re-exporting them as shoes and belts,'' says CITES's Berney. ''The same occurred with live birds.'' But pressure from a CITES investigative committee and international trade threats got Italy moving, Berney adds, and now ''they've completely changed their attitude and have a solid inspection program.'' Compared to 10 years ago, Latin America has also registered a number of successes, especially in reducing the illegal bird trade. Experts cite Paraguay, Uruguay, and Argentina in particular. Mexico, however, is a case that most experts agree has only gotten worse. ''The illegal trade in Mexico is as active as it ever has been, and probably worse,'' Hemley says. ''But we also have to recognize that Mexico is in a real challenging position. It is a country of incredible species diversity, with the world's single biggest wildlife market [the US] right next door,'' she says. Mexican officials insist, however, that a string of actions taken this year points to a new determination to stop the trading in endangered species. The law enforcement agency assigned to enforcing environmental legislation, including that on animal trade, has been beefed-up. The Federal Attorney General for Environmental Protection (PROFEPA) organized last month's raid on Sonora Market, recently jailed traffickers in sea turtle eggs, and is targeting other hot points of animal trafficking, such as ports, airports, and the US-Mexican border. ''We are sending a signal to every segment of society that we are serious,'' says Victor Ramirez Navarro, PROFEPA's assistant attorney for natural resources. ''We are noticing an improvement,'' says Jesus Bustamante, a Texas field agent for the US Fish and Wildlife Service and a longtime animal-trafficking specialist. ''The smugglers on the Mexican side used to act with impunity, but now we see them taking measures to keep from being discovered,'' he says. Yet not everyone is impressed. ''Such [government actions] are only cosmetic and serve no purpose if there isn't the political will to hit the trafficking networks behind this trade,'' says Graciella de la Garza, for six years until 1992 Mexico's environmental inspection and enforcement chief. ''I resigned then because I was not given the political backing to really uphold the law, and that situation hasn't changed since,'' she says. Ms. de la Garza's efforts to tackle the ''sons of very prominent politicians,'' whom she says run Mexico's most lucrative animal trading, were thwarted by high-level pressures. A CITES investigation in 1988, for example, cited David Ibarra Cardona, the son of a former finance minister, for heavy trafficking of animals into the US. ''And the same people continue in the same activities, untouched,'' de la Garza says. Earlier this year Jorge Hank Rhon, member of one of Mexico's most powerful political families was caught smuggling ivory and spotted-cat pelts into Mexico from Asia. He has been released on bail pending trial. And he is known to keep endangered animals. Environmental laws need teeth Mexico cannot be considered a serious opponent of illegal animal trafficking, de la Garza says, as long as the country's new environmental laws are not accompanied by stiff penalties - including prison terms. ''We've been seven months without the regulations to back up'' Mexico's reorganized environmental legislation, she says. Officials like Mr. Ramirez say they don't blame environmentalists for their skepticism about Mexico's determination, but they ask to be judged by upcoming actions, not the past. One plan that Mexican officials now emphasize is a tandem effort to dry up the illegal animal market through tougher police enforcement and punitive action, while helping rural communities and local populations to develop a legal market in sustainable species. ''I'm not against people in North Dakota having a parrot in the home if it can be done legally and in a way that is profitable to our rural population and guarantees a sustainable existence to the [bird] species,'' says Arturo Argueta, conservation and sustainable-use coordinator for Mexico's National Ecological Institute. This policy puts Mexico in the center of a hot international controversy over whether development of a legal animal trade in supposedly ''sustainable'' species is really feasible, especially in developing countries with limited resources. ''We are very skeptical about the whole notion of sustainable use and sustainable trade in animals,'' says John Grandy, vice-president for wildlife and habitat protection at Humane Society International in Washington. ''What really ends up happening is that the 'use' is put into practice, while 'sustainable' gets left at the door,'' he says. The notion of ''sustainability'' is senseless in countries like Mexico, de la Garza adds, where there are no in-depth studies on just what ''sustainable'' harvest levels are for each species, and little enforcement of capture regulations. But organizations like the WWF and CITES favor development of legal, regulated markets where species are shown to be sustainable. ''People have kept birds in their homes for thousands of years,'' Mr. Argueta says. ''I don't think we today can stop that desire, but I think we can develop and regulate trade so that these species will be around for future generations. ''We need to educate people in both the source and consumer countries that if the last examples are taken from the forest so a few individuals can possess them, then everyone loses,'' he says.